Agreed that the T-34 was the most prolific, but disagree as to it being the best tank of the war. The T-34 was incredibly simple and used the American chassis/suspension design which made it reliable. But even the T-34 had its problems. The driver could not see and had to open the frontal hatch to maneuver or rely upon the tank commander to steer. Their gun was fantastic but loading was complicated due to lack of internal space, making their rate of fire ridiculously slow. They were used at Kursk in 2 ways: to absorb German rounds and to ram German tanks.
The best medium tank of WW2 had to be the Panther Mk. 5.